1. Field of the Invention
The present invention relates to a liner hanger device of the type used to hang a liner in a surrounding well bore and, specifically, to improvements in the system by which the gripping slips of the device are mounted and supported on the exterior of the device.
2. Description of the Prior Art
Liner hangers are typically used in well operations to attach an inner string of well pipe to the lower end, or at some other point, within a larger diameter well pipe or casing. The liner hanger typically comprises a device which is attached to the liner and which includes a set of pipe gripping slips which are arranged to be expanded into gripping engagement with the interior of the larger diameter pipe to thereby secure the smaller diameter pipe or liner thereto. The term "pipe" will be understood to mean pipe, tubing or casing of the type used in well bore operations. After hanging the liner, the liner will usually be cemented, which requires the circulation of fluids through the interior of the liner and upwardly about the exterior of the liner between the liner and the outer casing.
In many cases, liners comprise long and heavy strings of pipe extending below the hanger and thus require large slip contact areas in order to assure effective attachment of the liner within the existing casing. Because of the close clearances which many times exist between the liner and the surrounding casing, or open hole in some cases, if sufficient slip area is provided to support such a long and heavy liner string, this will frequently tend to close off the annular space between the liner and surrounding well bore which, in turn, severely restricts the flow of fluid which is being circulated.
U.S. Pat. No. 3,195,646 to C. C. Brown, issued July 20, 1965, shows a liner hanger which employs multiple cones, each of which has a plurality of spaced-apart cone segments. The cones segments are spaced-apart to provide pathways or spaces which provide increased circulating capacity. The liner hanger has two staggered sets of gripping slips, with three slip segments in each set. The gripping slips are vertically aligned with mating cone segments and the staggered design provides a large by-pass area for easy running and free circulation of fluids. The large distributed slip contact area also reduces stress in the supporting casing.
Because of the multiple cone, staggered slip arrangement utilized, the gripping slips were mounted on the exterior of the hanger by a slip support collar. Each slip was secured to its respective slip collar by means of a spring arm which normally biased the slips inwardly toward the exterior surface of the hanger. While the mounting method shown in U.S. Pat. No. 3,195,646 works well in practice, the slip support collars require milling and welding and add to the cost of building and assembling the tool.